Monday, February 20, 2012

A group of emperor penguins
exits the water at Cape Washington. The birds are regularly capable of
going down to depths of 500 meters for five to 12 minutes at a time.

A big breath

By Peter Rejcek, Antarctic Sun Editor

Posted February 10, 2012

Leopard seals are sort of the Great White Sharks of the
Southern Ocean — viciously effective and elusive predators that are
notoriously difficult to study. Never mind all the sharp teeth.

Two years ago, Dr. Paul Ponganis and his research team moved their main base of operations from near McMurdo Station
to Cape Washington, 300 kilometers away, where an emperor penguin
colony goes to breed every Antarctic summer. They had hoped that during
their ongoing research into emperor penguin physiology that one of the
handful of leopard seals that prowl around the colony might be used for
behavioral research.

But they never got close.

“They are a poorly studied animal. Not many people get
access to them,” Ponganis said. “I knew it was going to take a lucky
year at Cape Washington to do this leopard seal study.”

The researchers are particularly interested in the penguins
for their innate diving abilities. Over the years, the scientists have
collected plenty of data on how fast the emperors can swim, the number
of strokes they take on a dive, and just about any other tangible detail
imaginable.

Photo Credit: Paul Ponganis

A leopard seal on the prowl at Cape Washington.

Photo Credit: Paul Ponganis

Emperor penguin chicks still under their parent's brood patches early in October at Cape Crozier.

They’ve learned the birds are regularly capable of going
down to depths of 500 meters for five to 12 minutes at a time. They’ve
been able to calculate the air volume in the birds’ lungs while they are
diving. The deeper the birds go, the bigger the gulp of breath in their
lungs. The oxygen from the lungs is then carried through the
bloodstream to the animal’s muscles.

The latest question has to do with the deepest dives, which
presumably require more oxygen to be extracted from the lungs and
circulated through the body. In theory, that should require the heart to
pick up the beat.

“Is the pattern during the deep dives different?” Ponganis
said. “Is the overall heart rate for a deep dive of equivalent duration
to a shallow dive lower, the same or higher?”

Much of the team’s previous research into emperor penguin
diving physiology has taken place on the sea ice that covers McMurdo
Sound through the early part of the Antarctic summer. Dubbed Penguin
Ranch, the study site is located over an area where the water column is
only about 100 meters deep.
The move to Cape Washington allowed the scientists to study
swimming behavior five times as deep. For the last two years, working
from a field camp on the coast of Victoria Land, they outfitted the
birds with electrocardiogram recorders to monitor their heart rates as
they plunged to great depths in search of food.
Ponganis and his team know from their work at Penguin Ranch
that the birds hyperventilate before a dive, revving their heart rate
as high as 220 beats per minute, before it slows down to about 60 beats.

“They’re really oxygenating themselves, storing things up
to get ready for this dive. They’re really fired up. When they dive, it
plunges back down,” he explained.

The heart rate on shallow dives can slow markedly, as time
drags on. After 10 minutes or more, the heart drums out a beat 20 times a
minute. On one dive, an emperor stayed under water for a record 27
minutes, possibly trapped from reaching the surface because a hole in
the ice had closed or a leopard seal was prowling about.

“I wish we had a heart rate monitor on that one,” Ponganis
said, estimating a heart rate of five beats a minute. “This animal is
just eking things out. That’s an extreme situation, but they are capable
of doing that.”
So, what does all this have to do with leopard seals? While
a major focus of the study is on diving physiology, the scientists are
also interested in colony population dynamics. The group monitors the
seven emperor penguin colonies around the Ross Sea.

In the case of Cape Washington, home to between 15,000 and
20,000 breeding pairs, the researchers wondered if the leopard seals
affect the Cape Washington colony through predation.
The plan had been to locate a seal, sedate it, and put a
digital backpack camera on the animal capable of taking up to 10,000
images. A radio transmitter on the instrument package would help the
scientists relocate the animal and recover the camera.

No one even knows how many penguins a leopard seal
typically consumes in a day, Ponganis noted. “If we take one picture a
minute, we would get every capture,” he said.

Photo Credit: Paul Ponganis

An aerial overview of Cape Washington and the colony..

Ponganis said it is highly unlikely that the leopard seals
alone could threaten a colony, but it is one of many factors that must
be understood if scientists are to properly assess how the emperor
penguins will respond to a changing climate.

The physiology work is also part of that assessment, he
explained. Are the emperors already pushing the limits? If so, how would
changes to the environment affect them? Some scientists believe the
emperors are already being affected, calling for their protection.

But studying penguins isn’t just about helping save one
species. Medical science can also learn a thing or two from the diving
physiology of animals like the deep-diving emperor or some mammals like
seals.
“The big thing in both emperors and seals is that they can
tolerate levels of oxygen that are so low, and levels of blood flow that
are so low, we would have serious tissue damages, strokes, all sorts of
problems,” Ponganis explained.

In stroke victims, for example, a lot of tissue damage
actually occurs when blood flow returns to an organ that had its supply
temporarily cut off. Such oxidative stress can produce free radicals —
sort of rogue molecules — that can damage cells. In recent years, there
has been a big push in medical science to treat such conditions with
antioxidants, molecules capable of “scavenging” free radicals.

Studies of emperors at Penguin Ranch and other research on
seals have found that the animals have elevated antioxidant levels,
particularly of a molecule known as glutathione, which is also important
in recycling other antioxidants, according to Ponganis.

“Essentially, they have this system that as oxygen free
radicals form, they can scavenge them and break them down and prevent
any of the deleterious effects of any of these oxygen free radicals,”
Ponganis explained.
“Research on penguins and marine mammals can provide
insight into the processes that are going on in human patients, and
eventually lead, even if it’s tangential, into some improved therapies,”
he added.